Degenerative Myelopathy of Dogs:
Degenerative myelopathy of dogs, also called chronic degenerative radiculomyelopathy, is a slowly progressive, noninflammatory degeneration of the axons and myelin primarily affecting the white matter of the spinal cord. It is most common in German Shepherds, Pembroke Welsh Corgis, Boxers, Rhodesian Ridgebacks, and Chesapeake Bay Retrievers, but is occasionally recognized in many other breeds. The cause is a mutation in the superoxide dismutase1 (SOD1) gene, inherited in an autosomal recessive pattern with incomplete penetrance. It is similar to familial amyotrophic lateral sclerosis in human patients. Pathologically, there is noninflammatory degeneration of axons in the white matter of the spinal cord, which is most severe in the thoracic region.
Affected dogs are usually >8 yr old and develop an insidious onset of nonpainful ataxia and weakness of the pelvic limbs. Spinal reflexes are usually normal or exaggerated, but in advanced cases there is flaccid tetraparesis and hyporeflexia reflecting lower motor neuron involvement. Early cases may be confused with orthopedic disorders; however, proprioceptive deficits are an early feature of degenerative myelopathy and are not seen in orthopedic disease.
Myelography or MRI and CSF analysis are essential to exclude compressive and inflammatory diseases. A DNA test based on the SOD1 gene is available on the Orthopedic Foundation for Animals (OFFA) website (
http://www.offa.org). Dogs that are homozygous for the mutation are at risk of the disease and will pass one copy of the mutant allele to their offspring. Heterozygotes are at low risk of the disease but have a 50% chance of passing one copy of the mutant allele to each offspring. Homozygous normals are at low risk of the disease and will not pass the mutation to offspring.
There is no specific treatment and no evidence that glucocorticoids, other drugs, or supplements alter the course of the disease. Most dogs are euthanized because of disability within 1–3 yr of diagnosis.